Lubricating oil is circulated through engines in order to reduce friction between moving parts and to remove heat from pistons, bearings and shafts.
Oil pumps are known to include a recirculation valve for controlling or regulating the delivery of oil to an engine. Such recirculation valves are designed to open when the pressure of oil in an engine reaches a predetermined value and prevent excess oil flow being delivered to the engine main gallery.
One example of a known recirculation valve is a directional control valve having a control chamber, a spring and a spool. When the pressure of oil in the engine exceeds the pressure in the control chamber by more than the compression pressure of the spring, the spool moves beyond the break edge of the pump, allowing oil to flow from the outlet of the pump to the inlet. In this way excess oil is recirculated and not delivered to the engine main gallery or other oil consumers within the lubrication system.
Since such recirculation valves only open at a single, predetermined regulation pressure, which is controlled by the compression pressure of the spring, it is only possible to regulate the engine oil pressure at a single, predetermined feedback pressure. This can result in a delivery of oil flow that is greater than the optimum amount at a given operating condition. For example, during operating conditions where the piston cooling jets are inoperable a much lower pump output can be tolerated. Reducing the pump output to the ideal optimum reduces the work that the pump must do and in turn reduces the parasitic drag on the engine, leading to increased engine efficiency.